The present invention relates to a process for purifying a composition (I) comprising at least one cyclic ketone having from 7 to 16 carbon atoms, which comprises thermal treatment of the composition (I) with at least one catalyst comprising at least one transition metal and further purification by means of a process selected from the group consisting of distillation, extraction and crystallization. The present invention further relates to a process for preparing cyclododecanone, which comprises such a purification, and the use of at least one catalyst comprising at least one transition metal for purifying a composition (I) comprising at least one cyclic ketone having from 7 to 16 carbon atoms by thermal treatment of the composition (I) with the catalyst comprising at least one transition metal.
Cyclic ketones are required in high purity for various applications. Due to the production process, cyclic ketones frequently comprise impurities, for example impurities having oxygen-comprising groups which can be removed only with difficulty by means of conventional purification processes such as distillation or crystallization. Conventional purification processes for such separation problems are therefore complicated and costly.
Thus, for example, cyclododecanone is an important intermediate for the preparation of, for example, laurinlactam, dedecanedicarboxylic acid and polyamides derived therefrom, for example Nylon 12 or Nylon 6.12.
Cyclododecanone is prepared, for example, by air oxidation of cyclododecane in the presence of boric acid to form cyclododecylborate, hydrolysis of the borate to form cyclododecanol and subsequently dehydrogenation of the cyclododecanol. Cyclododecane itself is obtained by full hydrogenation of cyclododecatriene. A description of this industrial process for the synthesis of cyclododecanone may be found, inter alia, in T. Schiffer, G. Oenbrink, “Cyclododecanol, Cyclododecanone and Laurolactam” in Ullmann's Encyclopedia of Industrial Chemistry, 6th Edition, 2000, Electronic Release, Wiley VCH.
A further process starts out from the epoxidation of cyclododecatriene, with cyclododecanone being obtained from the epoxide by hydrogenation and rearrangement. Such processes are disclosed, for example, in EP 1 018 498 A2. DE 103 44 595 A and DE 103 44 594 A describe processes for preparing cyclododecanone in which oxidation with dinitrogen monoxide is carried out in one process step.
In all processes, the purity of the crude products is not sufficient for some applications without additional purification. Organic compounds having oxygen-comprising groups in particular are frequently comprised in the products obtained in unacceptably large amounts. In these cases, a very complicated purification, for example by multistage distillation and/or crystallization, is therefore necessary.